This invention relates to the forming of contacts on a diamond which is used as a detector of ionizing radiation.
Counting diamonds are diamonds which can be used for detecting high energy ionizing radiation or energetic nuclear particles such as alpha particles, protons, or neutrons. Such diamonds are normally insulators or semi-conductors, to which an electrical potential is applied via spaced electrical contacts on the diamond. Ionizing radiation incident on the diamond causes the liberation of free charge carriers which are collected via the contacts and measured by means of an electrical circuit.
When a metallic conductor is attached to a non-conductor, the difference in the work functions of the metal and the non-conductor will result in a potential at the contact surface which will cause a uniform electric field spreading into the insulator. Depending on the direction of the field and the charge polarity of the carriers the field either aids or impedes the collection of the carriers. Furthermore, there may exist surface and intersurface electronic states which will further affect the field and the collection of carriers. The more intimate the contact between the non-conductor and the conductor material the more likely it is that the carriers will be transferred to the electronic circuit without hindrance.
Kozlov (U.S. Pat. No. 3,665,193) discloses a natural diamond radiation detector, with various kinds of contacts being applied to a diamond crystal to achieve electrical contact therewith. The contacts comprise metals such as gold, silver or platinum, or graphite, applied to the surface of the diamond. Typically a suspension containing the contact material is applied to the diamond, which is then heated to form a metal contact on the surface of the diamond. In another example, a gold layer is evaporated onto the surface of the diamond. It is believed, however, that such contacts are not ohmic.